Metering devices or metering pumps which are currently available for supplying fluid material in a specified amount typically supply the fluid material in spurts or a series of injections, rather than continuously. The application of material in such a discontinuous fashion is a disadvantage in that the material being applied by the device to the desired surface may be uneven. Additionally, such metering pumps are often large, and difficult to use in a small manufacturing space. The large size of such devices also results in their relative high cost.
Conventional metering devices for fluid material have the further disadvantage that they do not reliably provide a specific amount of material at the desired location. Such conventional devices often provide material in a pulsed flow, instead of a continuous flow. For example, it may be desirable to have a specific thickness of material applied to ensure a desired use or result from the material. The failure of such devices to provide a regulated and continuous amount of material may result in increased waste of the material being applied, as well as waste of the item to which the fluid material is applied. The failure to apply specific amounts of material is often due to a clog or plug of material which may form within the device and result in improper performance, or the pulsing application referred to.
Additionally, special metering conditions often require the application of different fluid materials having variable viscosities or materials with unusual rheological characteristics. Dispensing such materials at low or variable flow rates on a consistent basis has not been possible using one conventional metering device. Typically, separate metering devices are used to apply each of the different viscosity fluid materials. The additional complication of providing such fluid materials in small, but specified amounts, has also not been readily possible using a single currently available metering device.